1. Field of the Invention
The present invention relates to a scanning probe microscope which measures various physical properties such as the surface shape or viscoelasticity of a sample through a scanning with a probe approaching the surface of the sample, and an optical axis adjustment method for the scanning probe microscope.
2. Description of the Related Art
A scanning probe microscope (SPM) measures the surface shape of a sample with a probe, which is attached to the tip of a cantilever, approximate to or brought in contact with the surface of the sample. It is known that an optical lever type SPM, in which laser light is emitted on the back surface of the tip of the cantilever, and reflecting light thereof is detected, is adopted as the scanning probe microscope. In the optical lever type SPM, a positional deviation of the reflecting light of the light emitted on the cantilever is detected as the displacement of the cantilever, and the surface of the sample is scanned while performing a feedback control to keep a displacement quantity of the cantilever constant. A feedback control signal is used for calculating a height or a physical property of the sample, and the physical property such as the surface shape or viscoelasticity of the sample can be measured.
In the optical lever type SPM, the laser light should accurately focus on the cantilever such that the intensity of the reflecting light reflected from the cantilever is maximized. There is a need to perform an “optical axis adjustment” in which the position of a detector detecting the reflecting light is adjusted. In this regard, a configuration is developed in which an optical microscope and a video camera are provided immediately above the cantilever, a beam splitter is disposed on the optical axis of the optical microscope, and the laser light emitted from a side is led downward through the beam splitter and emitted on the cantilever. An example of such configuration is disclosed in JP-A-2012-225722. According to such configuration, the position of the laser light can be directly checked with the optical microscope since a part of the laser light is directed upward through the beam splitter, and thus the optical axis adjustment is facilitated.
In a case where the laser light is obliquely emitted on the cantilever, the spot position of the laser light which can be checked with the optical microscope is not matched with the position of the laser light which is actually emitted on the cantilever, and further the laser light emitted on the cantilever cannot be directly viewed with the optical microscope. Accordingly, there is a problem that the optical axis adjustment should be performed by instinct, and a skill is required. In this regard, a configuration is developed in which the laser light emitted on the cantilever can be viewed by providing an auxiliary emission surface for helping the observation image of the optical microscope which comes into focus under the cantilever, and thus the optical axis adjustment is facilitated. An example of such configuration is disclosed in JP-A-2014-044144.
However, in the case of the configuration described in JP-A-2012-225722, the beam splitter (reflecting portion) is disposed on the optical axis of the optical microscope and blocks the center of the optical axis of the optical microscope, and thus there may be a problem that a resolution performance of the microscope is degraded. This configuration cannot be applied to a scanning probe microscope which obliquely emits the laser light on the cantilever.
In the case of the configuration described in JP-A-2014-044144, it is necessary to provide the auxiliary emission surface, and thus there may be a problem that an apparatus is complicated or is difficult to be miniaturized. It is still necessary to be skilled or take time for the optical axis adjustment since an operator manually performs the optical axis adjustment while viewing the laser light.